<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Demo - error-component</title>
</head>
<body>
<div id="parent">
    <error-component kind="error">
        This is an error message.
    </error-component>
    <error-component kind="warning">
        This is a warning message.
    </error-component>
    <error-component>
        This is a default message.
    </error-component>
</div>
<script>
class ErrorComponent extends HTMLElement {

    constructor() {
        super();
    }

    connectedCallback() {
        this.root = this.attachShadow({mode: 'open'});
        this.templates = document.createElement('div');
        this.container = document.createElement('div');
        this.root.appendChild(this.templates);
        this.root.appendChild(this.container);
        this.templates.innerHTML = ErrorComponent.template();
        const kind = this.getAttribute(`kind`) || `none`;

        const template = this.templates.querySelector(`template.${kind}-type`);
        if (template) {
            const clone = template.content.cloneNode(true);
            this.container.innerHTML = '';
            this.container.appendChild(clone);
        }
    }

    static template () {
        return `
        <template class="warning-type">
            <style>
                .warning {
                    background-color: yellow;
                    padding: 15px;
                    color: black;
                }
            </style>
            <div class="warning">
                <slot>Error component<slot>
            </div>
        </template> 
        <template class="error-type">
            <style>
                .error {
                    background-color: red;
                    padding: 15px;
                    color: black;
                }
            </style>
            <div class="error">
                <slot>Error component<slot>
            </div>
        </template> 
        <template class="none-type">
            <style>
                .none {
                    background-color: gray;
                    padding: 15px;
                    color: black;
                }
            </style>
            <div class="none">
                <slot>Error component<slot>
            </div>
        </template>    
        `;
    }
}
customElements.define('error-component', ErrorComponent);
</script>
</body>
</html>